That's what a gearbox is for. You have a higher overall gear ratio when starting in first gear to keep the engine from stalling. Once the car is moving, you change gears to reduce the overall ratio until you reach the point where the wheels are rotating at a speed which won't cause the engine to stall, and the engine is turning at sufficient RPM to keep the car moving at a constant travel speed.

When you are accelerating to speed, unless you do it in a single gear, the analysis in the OP is not valid.